Kinematic Comparison of Spontaneously Generated Blinks and Voluntary Blinks in Normal Adult Subjects

Abstract

Purpose: Spontaneous and voluntary blinks share a common final neuromuscular pathway but have totally different purposes and have come under different evolutionary pressures. The purpose of this study is to compare quantitative blink kinematics (down-phase duration, amplitude, peak velocity, and lid-closure duration) of spontaneously generated blinks with voluntary blinks in normal adults. Methods: Spontaneous and voluntary (tone generated) blinks of the right eye of 7 subjects were studied by a modified scleral search coil technique. Automated analysis of each blink kinematic was performed and statistical analysis of pooled data was undertaken. Results: All kinematics of voluntary blinks were greater than those of spontaneous blinks: duration (77.6 ± 10.0 milliseconds) was 17.6% longer, amplitude (43.1 ± 7.9°) was 40.8% larger, peak velocity (1288.6 ± 358.5°/ms) was 47.3% faster, and mean lid-closure duration (13.4 ± 4.7 milliseconds) was 61.4% longer (P < .001 in all cases). Conclusion: Kinematics of voluntary and spontaneous blinks are significantly different, reflecting their different supranuclear control. This quantitative study confirms previous qualitative observations and clearly separates these categories of eyelid movement as distinct, with spontaneous blinks serving a purely physiologic function and voluntary blinks being a part of facial expressivity.